1. Field of the Invention
The present invention relates to industrial filter apparatus, and especially to tubular or "candle" filter devices.
2. Description of Related Art
It is common today to employ tubular filters in a variety of industrial filtering applications. These filters generally comprise a cylindrical sleeve of filtration media open at both ends which is slid over an inner perforated tube.
When a pressure differential is established across the filter, fluid flows through the filtration media and filtrate is removed. In order to prevent by-passing of unfiltered fluid around the sleeve, it is important that the ends of the sleeve are tightly sealed to the ends of the tube to avoid leakage of solids through the ends of the sleeve.
Most applications employing tubular filters use a number of tubes mounted in parallel with each other in a tube bundle. The tube elements are joined at one end to a fluid conduit in the form of a tube sheet or manifold and may be attached at their opposite ends to a spacer grid to maintain their relative positions. For liquid fluid filtration, the entire tube bundle is then mounted in the filter, or merely submerged in the liquid to be filtered, to remove unwanted impurities.
Although these forms of filtration apparatus are quite effective, maintenance of the filtration media has proven problematic. It is often a burdensome procedure to seal each end of the filter sleeve individually to each tube. These seals are usually formed with a cord, waterproof adhesive tape, or one of a variety of removable clamping elements. Unfortunately, sealing in this manner is time consuming, burdensome, and sometimes ineffective at sealing certain types of filtration media.
One of the major improvements in filter media has been the development of expanded polytetrafluoroethylene (PTFE). Such a membrane product can be produced in a known manner, such as in accordance with the teachings of U.S. Pat. No. 3,953,566 issued Apr. 27, 1976, to Gore. This material forms a microporous structure which can be adapted to provide specific filtration properties in many different forms. Sleeves for tubular filters are commercially available from W. L. Gore & Associates, Inc., Elkton, Md., under the trademark GORE-TEX.RTM. Membrane Tubular Filter Sleeves. These products comprise an expanded PTFE membrane attached to a felt-like material ranging in thickness from 0.75 to 2.5 mm. For certain applications, this material may comprise a composite, with additional layers applied to the filtration media for improved durability or better filtration.
While the use of expanded PTFE membrane laminates as a filter media provides exceptional filtration properties and durability, they too are difficult to seal at each end. As is true with other membrane composite filtration media, if fluid tight seals are not created between the membrane filter media and the ends of the tubes, particles can seep under the surface of the membrane through the fabric membrane support material and into the filtrate. This seepage of particulate up the end of the sleeve can result in serious filter compromise. As a result, particular care must be exercised in covering and sealing the ends of such media to assure a leakage-free system.
Maintaining the integrity of the filtration media/tube interface is further complicated in filtration apparatus employing back pulsing or similar procedures to clean solids or filter cakes intermittently from the filtration media. The reverse flow of filtrate inherent in such procedures increases the likelihood of leakage under the membrane through the support fabric at its ends.
Accordingly, it is a primary purpose of the present invention to provide a filter sleeve which is pre-mounted on an end cap so as to allow for easy installation.
It is another purpose of the present invention to provide a pre-installed fluid-tight seal between the ends of a filter sleeve and a tube to resist leakage around the membrane and up the end of the filtration media.
It is a further purpose of the present invention to provide a pre-installed end cap on a filter sleeve which can readily interface with existing filtration apparatus.
It is still another purpose of the present invention to provide methods for producing and installing a filter sleeve of a filter tube which is both effectively sealed and readily installed.
These and other purposes of the present invention will become evident from review of the following specification.